Oil sand, such as is mined in the Fort McMurray region of Alberta, generally comprises water-wet sand grains held together by a continuous matrix of viscous bitumen. It lends itself to liberation of the sand grains from the bitumen, preferably by slurrying the oil sand in hot process water, allowing the bitumen to move to the aqueous phase. Oil sand slurrying generally takes place in large, stationary slurry preparation or mixing towers. Once oil sand slurry is formed, the slurry is pumped through a pipeline at least 2.3 km long to the bitumen extraction facility.
During pipelining of oil sand slurry to extraction facility, the oil sand slurry undergoes conditioning, namely, ablation of oil sand lumps, liberation of bitumen from the oil sand, entrainment of the bitumen by air bubbles, and the coalescence of bitumen droplets. This allows the bitumen to be separated out more readily. The conditioned slurry is then temporarily retained under quiescent conditions in a large gravity separation vessel (referred to as the “PSV”) housed at the bitumen extraction facilities, where the sand settles and is removed as an underflow, together with some bitumen and water, and the aerated bitumen, contaminated with water and solids, including fines, rises and is recovered as froth.
These deep cone PSVs are very large, approximately 30 meters in diameter, so as to provide the large separation area required to process 8000 tonne per hour oil sand. The PSV is also 35 meters tall to assure free flow of coarse solids to the centrally located bottom discharge. When filled with oil sand slurry, each PSV weighs up to 25,000 tonnes and is suspended on 12 friction piles extending ˜40 meters below grade.
Bitumen extraction facilities housing these large PSVs have traditionally been located removed from the actively mined mine sites. Further, as the actively mined mine sites become more remote as the mine faces recede, the distance that the oil sand slurry must travel from the mine face to extraction and the distance that the separated sand must travel to sand disposal sites frequently exceeds 10 km. It is expensive to transport massive quantities of sand over long distances by pipeline, considering the high energy requirement per ton/km, the high cost of maintenance due to abrasion, as well as the capital cost of pipelines, pumps and auxiliary equipment.
The present invention uses a countercurrently operating assembly comprising a plurality of sand/liquid separators, which assembly is preferably relocatable, to separate out sand from bitumen, which may be configured so as to minimize the distance of sand transportation. Further, the present invention recycles water from tailings deposits thereby conserving water and reducing the need for heated water.
The present invention provides at least one of the following benefits:                1. reduced cost of sand transportation;        2. increased bitumen recovery from oil sand; and        3. reduced heat energy requirement, due to the displacement of warm middlings in the tailings stream with cold “beach run-off”, i.e., water from tailings deposition ponds.        